This invention generally relates to water jet-propelled boats or other watercraft. In particular, the invention relates to jet-propelled boats or other watercraft which have a pivotable steering nozzle arranged to receive the pump discharge and divert the discharged water in a desired direction.
It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) the hull. An impeller is mounted on a shaft driven by a drive shaft of the motor, and is housed in a duct having an inlet and an outlet. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the duct. The water discharged from the duct outlet produces a thrust which propels the boat forward.
In addition, it is known to provide a mechanism for diverting the discharged water flow to one side or the other of a midplane, thereby enabling the boat operator to steer the boat to the left or right during forward propulsion. One such mechanism is a steering nozzle pivotably mounted to the duct and in flow communication with the duct outlet. Preferably the pivot axis of the steering nozzle lies in the midplane. As the steering nozzle is pivoted to the left of a central position, the water flow out of the duct is diverted leftward, producing a thrust which pushes the water jet apparatus and the boat stern to the right, thereby causing the bow of the boat to turn to the left. Similarly, the boat bow turns to the right when the steering nozzle is pivoted to the right of the central position. The overall length of the propulsion unit is reduced when the steering function is accomplished by the discharge nozzle. In other words, the stator discharge is drawn together by a converging cone which also pivots to the sides for steering.
It is also known to provide a mechanism for reversing the direction of the water flow exiting the steering nozzle. In accordance with some known designs, the reverse gate is not steerable, i.e., the reverse gate is pivotably mounted to the fixed stator housing or exit nozzle. In the up position, the reverse gate is clear of the water flow exiting the steering nozzle; in the down position, the reverse gate obstructs the water flow exiting the steering nozzle and reverses the rearward flow component. Some non-steerable designs also reverse the lateral flow component; others do not. The non-steerable reverse gate designs which reverse the lateral flow component cause the rearward-moving boat to turn left when the steering nozzle is turned to the left and to turn right when the steering nozzle is turned to the right.
During pivoting of the reverse gate from its stored position to its fully deployed position or vice versa, the reverse gate must clear the aft upper edge of the steering nozzle. Typically, the center of rotation of the reverse gate is located at the intersection of horizontal plane which bisects the steering nozzle and a vertical plane which intersects the pivot axis of the steering nozzle. The greater the height of the steering nozzle, the greater the radius from the reverse gate pivot axis to the forward edges (upper and lower) of the reverse gate must be in order to ensure that the forward edge of the reverse gate clears the aft upper edge of the steering nozzle. Thus there is a need to provide a steering nozzle having a reduced vertical height, which would allow a corresponding reduction in the radius from the pivot axis to the forward edges of the reverse gate.
A reduction in the latter radius reduces the overall length of reverse gate measured from its pivot axis to its aftmost point. Additionally, the amount of vertical clearance which is needed for the reverse gate in the fully up or stored position would be reduced. This is beneficial in boats designed with a swim platform extending in cantilever fashion from the stern. Even for boats which do not incorporate structure overhanging the stored reverse gate, it is desirable to reduce the vertical height of the stored reverse gate, and the length of the deployed reverse gate, to minimize the extent to which the reverse gate presents an obstacle.
The present invention is directed to a jet-propelled boat comprising a water jet propulsion unit having a low-profile steering nozzle. In particular, the steering nozzle has an inlet opening with a width greater than its height, the vertical height of the steering nozzle inlet is reduced without reducing the volumetric flow rate through the inlet. This reduction in the height of the steering nozzle allows a corresponding reduction in the radius from the reverse gate pivot axis to the forward edges (upper and lower) of the reverse gate without compromising clearance vis-à-vis the aft upper edge of the steering nozzle.
In accordance with one preferred embodiment of the invention, the water jet propulsion system comprises a flow-through housing having an impeller section, a convergent section having a discharge aperture, and a cup-shaped extension; an impeller which is rotatable within the impeller section of the housing; and a steering nozzle pivotably mounted inside the cup-shaped extension for pivoting about an axis. The steering nozzle has an inlet opening with a width greater than its height, a laterally convergent section extending rearward from the inlet opening, and an outlet opening. Preferably the outlet opening of the steering nozzle is generally circular. The steering nozzle further comprises a second section having a passage which is generally cylindrical or slightly convergent. The second section ends at the outlet opening.
In accordance with a further feature of the preferred embodiment, a support post extends radially outward from the steering nozzle, and a steering arm extends laterally and forward from the support post. A portion of the steering arm extends outside of and overhangs a portion of the cup-shaped extension. Preferably the steering nozzle, support post and steering arm are formed as one cast piece. A longitudinal reinforcement rib can be integrally formed on the exterior of the steering nozzle, integrally connected to the support post.
The steering nozzle is pivotably mounted inside the cup-shaped extension by means of a pair of coaxial pivot pins placed at the top and bottom of the extension. In cases where the impeller shaft is inclined, i.e., not horizontal, the pivot pin axis is preferably perpendicular to the impeller axis of rotation, while the centerline axis of the steering nozzle is preferably horizontal, i.e., not parallel to the impeller axis of rotation. In accordance with the preferred embodiment, this is accomplished by fabricating a steering nozzle having a centerline axis which is not perpendicular to the common axis of the pivot holes which receive the pivot pins. In cases where the impeller shaft is horizontal, then the centerline axis of the steering nozzle is preferably coaxial with the impeller axis of rotation.
The invention is further directed to a jet-propelled boat having a water jet propulsion system of the foregoing type.